All of them really. My least favorites are twitter, facebook,, Google Plus, and then Tumblr based purely on platform.

140 characters and something that literally gets buried in minutes isn't very social. It's a chat room with a character limit. A really, really, really shitty chatroom. Facebook hides most of the shit you want to read and posts your friend's inane copypasta. G+ is facebook minus anything social, but you can find decent stuff on it. Tumblr is the new livejournal. As a blog platform it's ok, but it's like if you're going to do a blog, get a wordpress site or something.

Youtube has a decent purpose if you ignore comments. Vine/instagram... Show pictures or gifs? NBD.

As for the clusterfuck of idiocy... Tumblrtards take the cake. And the first place the infect afterward was Twitter. Followed by Facebook.

The only reason I use Tumblr is because of my fandom blog. Also Twitter's kinda boring. I don't like Instagram/Vine because the people on there get on my nerves. A lot. And Facebook is crowded with middle-aged adults and old women... I don't really like any of them that much. Youtube is okay, it still has good videos, just don't check the comments if they bother you.